1. Field of the Invention
This invention relates to a small-sized liquidproof battery-powered appliance such as a waterproof electric shaver or an electric toothbrush driven by a miniature motor whose power source is a rechargeable secondary battery incorporated in the appliance. More particularly, this invention relates to a liquidtight structure of such an appliance and relates also to a gas venting structure of the appliance for venting gas generated from the secondary battery to the outside of the appliance.
2. Description of the Prior Art
It is commonly known that, in a liquidproof battery-powered appliance having a secondary battery incorporated in its liquidtight body casing, hydrogen gas is generated from the secondary battery during discharging and recharging the secondary battery, as described in Japanese Utility Model Publication No. 47-39542 (1972) or Japanese Utility Model Publication No. 58-5329 (1983). The hydrogen gas may be generated in a very large amount due to an unusual operating condition such as an overcharge or an overdischarge and may be jetted from a battery safety valve to fill the internal space of the body casing of the appliance. In such a case, it is necessary to immediately exhaust the hydrogen gas to the outside of the appliance.
A gas venting structure for exhausting hydrogen gas to the outside of a liquidproof battery-powered appliance such as a waterproof electric shaver is known. As a prior art example of such a structure, Japanese Patent earlier publication No. 60-24882 discloses a structure for exhausting hydrogen gas generated from a storage battery in an electric shaver and accumulating in a body casing of the electric shaver.
According to the disclosure of Japanese Patent earlier publication No. 60-24882 cited above, a positive terminal pin of the storage battery is shaped in the form of a small pipe and is locally spot-welded at its flanged base end portion to the positive electrode of the storage battery, and the flanged portion of the positive terminal pin is covered with a battery packing of rubber material covering the position electrode of the storage battery. Gas generated in the storage battery is exhausted from a gas vent hole provided in the positive electrode and accumulates in a gas reservoir formed inside the battery packing. The gas accumulating in the gas reservoir flows through a gap formed between the packing and the positive electrode into the positive terminal pin to be exhausted to the outside of the housing of the electric shaver.
A gas venting structure using such a hollow electrode terminal pin to vent gas generated inside an appliance to the outside of the appliance is also described in U.S. Pat. No. 4,451,980.
However, a prior art gas venting structure as described above has had the problem of an inevitable increase in the number of assembling steps since it includes many small parts including a packing covering the positive electrode of a storage battery and a hollow electrode terminal pin for venting gas. Also, the prior art gas venting structure has not been fully satisfactory from the aspects of securing the quality of connection parts and the tightness of seals.
Japanese Utility Model earlier publication No. 61-79457 discloses a liquidproof battery-powered appliance in which a battery unit constituted by the combination of a plurality of secondary batteries, a battery cap mounted on the upper part of these secondary batteries to prevent relative displacement of these secondary batteries, a rubber packing intimately covering the lower part of the secondary batteries and a packing casing fitting over the rubber packing is encased in a battery accommodation casing, and the battery unit encased in the battery accommodation casing is disposed inside a body casing of the appliance.
However, the disclosed appliance has also had the problem of an inevitable increase in the number of assembling steps resulting from an increased number of parts. Further, the disclosed appliance has required liquidtight seals at an increased number of locations.
On the other hand, a liquidtight structure for a battery-powered appliance of this kind is disclosed in, for example, U.S. Pat. No. 4,363,169. However, the liquidtight structure described in this U.S. patent requires various parts of complex shapes including an inner cover, a lifting cam member, an outer cover, a pawl and a dial in order to carry out both the function of mechanically holding the battery in position and the function of liquidtight sealing the battery insertion opening. Therefore, the proposed liquidtight structure has had the problem of a high manufacturing cost. Also, the proposed liquidtight structure has not been satisfactory in that venting of gas is not taken into consideration.